Typical ultrasonic flaw detectors are similar to oscilloscopes, and generally incorporate special features designed to help detecting and characterizing flaws in materials. Flaw detectors are widely used for material evaluation and they are designed as small, hand-held microprocessor-based devices suitable for both laboratory and industrial applications. A schematic block diagram of a typical ultrasonic flaw detector is illustrated in FIG. 1.
A typical, conventional flaw detector uses one channel pulse generator to excite an ultrasonic transducer and create sound waves (traveling mechanical vibration) propagating through the inspected material. Reflected echoes (energy) from the boundaries and/or flaws are converted by the ultrasonic transducer into electrical signals which are amplified, and sent to a receiver channel. The electrical signals are then digitized, filtered and displayed on a screen as ultrasonic waveforms (A-scans) that can be interpreted by the operator. Alarm gates (amplitude thresholds) are often employed to monitor signal levels at selected points in the A-Scan to flag echoes from flaws.
The conventional ultrasonic flaw detector technology is reliable and well accepted; it is also relatively simple to use, particularly for slightly oriented, accessible and relatively big flaws. Straight and angled beam testing is generally employed to find flaws. In many instances, however, simple display of A-Scans is cumbersome and difficult to interpret. Moreover, conventional hand-held flaw detectors do not offer imaging capabilities for flaw visualization and are typically limited to a single ultrasonic transducer. Since beam orientation is necessary for accurate flaw detection, conventional flaw detectors also use a series of angle wedges to cover a small range of beam orientated inspection.
With such a typical flaw detection configuration, it is not possible to visualize and adequately characterize small volumetric flaws. It is also more complex to reach flaws in hidden regions and visualize them at the same time. One way to produce real-time flaw visualization without moving the transducer in time-consuming raster scan pattern is to use echographic images based on phase-array technology using an array or matrix of ultrasonic transducers.
Ultrasonic phase-array probes generate focused beams by controlling the time delays of the excited ultrasonic waves which in turn are generated from a plurality of separate and spaced apart ultrasonic transducers such as piezoelectric elements. Beam focusing and steering is also achieved by phase-array probes at the reception of the returned echoes by applying the same control delay(s) as for the emission. These delays have a specific profile called focal law profile. Therefore, the ultrasonic beams can be focused and/or steered within a volumetric working space to probe for flaws and discontinuities in the material propagating the ultrasonic waves. Flaws in the body of material can be detected on the basis of ultrasonic echoes that are returned or deflected from such flaws. As phase-array beams are generated electronically, electronic raster scanning permits very rapid structural flaw imaging, flaw detection and volumetric characterization. Electronic raster scanning also allows to circumvent problems associated with a fixed mechanical lens of transducers, to eliminate all moving transducer parts, and to avoid many problems related to ultrasonic coupling.
Phase-array probes can create simple echographic sectorial scans (S-Scans) representation where multiple A-Scan signals with different angles are stacked and presented as a global electronic scan image. S-Scan can represent a color coded 2-D layout of the tested structure. It provides quick information since it gives the true depth representation and 2-D representation of the flaws.
Phase-array ultrasonic technology moved from the medical field to the industrial sector at the beginning of the 1980s. By the mid-1980s, piezocomposite materials were developed and made available to manufacture complex-shaped phase-array probes. The company R/D Tech Inc., whose address is 505, boul. du Parc-Technologique, Québec, Québec, Canada, G1P 4S9 has widely investigated and implemented the phase-array concept for industrial standardization and transfer of the technology. Phase-array development at R/D Tech Inc., has been based upon a series of portable phase-array instruments that can be operated in the field by a single operator, and collect data from engineering structures for remote analyses.
A need still exists for a hand-held, lightweight, portable flaw detection device that can be easily used to detect defects in materials and, then, to rapidly visualize these defects on a display, for example a LCD display, for better characterization, and in which simple display software algorithms can be used to locate and categorize the detected defects.